Method for regenerating brake linings

ABSTRACT

In order to regenerate a brake lining, preferably for a railway vehicle, a friction lining is worked by machining, starting from its worn surface, and provided with a three-dimensional surface profile. The profiled surface is then coated with an agglutinant, and a fresh friction lining substance is pressed on. The worn surface is preferably worked by profile grinding or profile milling, such that a profiled surface structure is produced having a teeth-like, trapezoidal or meander-shaped profile that is vertical to the surface, wherein the profile depth of the surface structure lies in the region of approx. 1-30 mm, preferably 5-20 mm. The profile is preferably oriented in one direction, crosswise to the main strain of the friction lining during braking.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of regenerating brake linings,particularly for railway vehicles.

2. Description of the Related Art

Brake linings have a friction lining attached to a lining carrier. Thefriction lining layer is worn away during the braking process as aresult of the frictional loading so that replacement of the used brakelining becomes necessary. Brake linings are commonly replaced before thefriction lining layer has been completely removed at the most stronglyworn position. For reasons of safety brake linings are generallyreplaced considerably before they are fully worn. For instance, liningson railway vehicles are commonly replaced when their friction lininglayer has been about 50% used up.

Although a large proportion of the friction lining layer thus remainsunused, the used brake linings are subjected to material recycling.

BRIEF SUMMARY OF THE INVENTION

It is the object of the invention to provide a method of regeneratingbrake linings, particularly for railway vehicles, that permits moreeconomical recycling of the used brake linings.

This object is solved in accordance with the invention by a method forregenerating brake linings, particularly for railway vehicles, in whicha friction lining layer is machined from its worn surface and providedwith a three-dimensional surface profile, the profiled surface is coatedwith a bonding agent and thereafter a fresh friction lining compositionis pressed on.

This method has the advantage by comparison with the known methods thata substantially greater proportion of the remainder of the frictionlining, which has not been worn away, can be reused for the regeneratedbrake lining. Any oblique wear which potentially occurs, i.e.non-uniform abrasion of the old friction lining layer, is fullycompensated for by the regenerating method in accordance with theinvention. Furthermore, the dust or chippings produced by grinding awayor milling away the surface of the friction lining can be reused, forinstance for road building purposes.

The three-dimensional surface profile creates a toothed transitionbetween the old friction lining composition and the newly pressed oncomposition. The lining thus formed can be worn away over the newlyapplied layer of friction lining composition, whereby use of the entirenew lining thickness is rendered possible. At no stage of the abrasionis a surface layer of which a major proportion comprises bonding agentused for braking purposes.

In one embodiment of the method in accordance with the invention theworn surface is machined by profile grinding or profile milling suchthat a profiled surface with a tooth-shaped, trapezoidal ormeander-shaped profile perpendicular to the surface is produced, theprofile extending, at least in sections, in a first direction on thesurface. In another embodiment the worn surface is machined by coarsegrinding such that an irregular surface structure with substantiallyelongate recesses is produced, the recesses which are formed extending,at least in sections, substantially in a first direction. This machiningprocess is performed successively in two intersecting directions in afurther embodiment. In the embodiments of the method in accordance withthe invention referred to above a surface structure is produced whichaffords a large area and into which the fresh friction lining, which issubsequently pressed on, engages, so that shearing away of the freshlining is prevented. The selection between the aforementioned surfacestructures or profiles is effected in dependence on the machiningprocess selected, particularly the tools which are used and the desiredfield of application of the regenerated brake linings.

An advantageous embodiment of the invention is characterised in that theprofile depth of the surface structure is in the region of about 1 to 30mm, preferably 5 to 20 mm. The profile depth of the surface structure isso selected that there is a minimal risk of shearing away and a goodconnection between the old friction lining and the newly appliedfriction lining composition. On the other hand, the profile depth is soselected that as large a proportion as possible of the old frictionlining composition can be reused, i.e. that as small a proportion aspossible is removed by the grinding process.

If the new friction lining layer is worn down beyond the transitionbetween the new and old friction lining compositions, the depth of theprofile results in the surface of the friction lining never having alarge proportion of bonding agent.

In a preferred embodiment of the method in accordance with the inventiona direction transverse, preferably at right angles, to the direction ofthe main loading of the friction lining during the braking process isselected as the first direction. The risk of the newly applied frictionlining composition shearing away from the old friction liningcomposition is thereby further reduced.

In one embodiment of the method the first direction is altered in aplurality of adjoining sections of the friction lining surface. Thisfeature further improves both the adhesion and also the shear resistanceof the applied friction lining composition.

One embodiment of the invention is characterised in that a worn frictionlining layer applied to a metal plate is worn down to a predeterminedresidual thickness such that the plate constitutes, together with theremaining friction lining layer, a sufficiently mechanically stablestructure for the further method steps. This exemplary embodiment findsapplication particularly in linings for railway vehicles or other largelinings with relatively thin carrier plates. The thin plate togetherwith a sufficiently thick residual lining serve as a carrier for theregenerated brake lining. Particularly in the case of those brakelinings in which the lining carrier is a thin plate and in which thefriction lining composition thus serves additionally to mechanicallystabilise the structure, the brake linings are replaced at a relativelyearly time at which the remaining frictional lining is stillsufficiently thick to stabilise the structure. In this application about30 to 60% of the friction lining composition is saved by the method inaccordance with the invention.

A substance containing phenol resin or rubber is preferably used as thebonding agent in the method in accordance with the invention.

Further advantageous embodiments of the invention are characterised inthe dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below in more detail by way of exemplaryembodiments illustrated in the drawings, in which:

FIG. 1 is a plan view of a brake lining machined in accordance with afirst exemplary embodiment of the regeneration method in accordance withthe invention, the brake lining being shown after termination of themachining;

FIG. 2A is a schematic sectional view through the brake lining shown inFIG. 1;

FIG. 2B is a schematic sectional view through the brake lining of FIG.2A after pressing on the fresh friction lining composition;

FIG. 3 is a plan view of a brake lining machined in accordance with analternative exemplary embodiment of the method in accordance with theinvention, the brake lining being shown after termination of themachining;

FIG. 4A is a schematic sectional view of the brake lining of FIG. 3; and

FIG. 4B is a sectional view of the brake lining in FIG. 3 after pressingon the fresh friction lining composition.

DETAILED DESCRIPTION OF THE INVENTION

The brake lining shown in FIG. I has a friction lining layer 3 appliedto a lining carrier 2. In order to regenerate the brake lining thefriction lining layer 3 is machined from its worn surface and providedwith a three-dimensional profile. The machined surface profile of thefriction lining layer 3 extends in a first direction 4 in theillustrated brake lining.

FIG. 2A is a schematic sectional view of the brake lining shown in FIG.1 along the line II. The original worn surface of the friction lining isshown by a chain-dotted line. The worn friction lining layer 3 is firmlyconnected to the lining carrier 2 by means of an intermediate layer 10.

In the exemplary embodiment illustrated in FIG. 2A, a three-dimensionaltooth-shaped surface profile 7 is produced by means of the machiningprocess. In alternative embodiments this profile can be sawtooth-shaped, trapezoidal or meander-shaped. The profile preferablyextends transversely to the principal loading direction during thebraking process. In the case of a saw tooth-shaped profile withperpendicular and oblique profile walls, the perpendicular profile wallspoint approximately in the direction of the force exerted by the brakelining during the braking process. This additionally increases theresistance to shearing away.

FIG. 2B is a schematic sectional view through the regenerated brakelining. After applying a layer 8 of bonding agent or adhesive to theprofile surface 7 a fresh friction lining composition 9 was pressed on.The fresh friction lining composition is pressed on in a thickness whichis more than half the overall thickness of the friction liningcomprising the old friction lining composition 3 and the fresh frictionlining composition 9.

FIG. 3 is a schematic plan view of a brake lining in which the surfaceof the worn friction lining layer is provided with a three-dimensionalsurface profile in accordance with an alternative exemplary embodimentof the method in accordance with the invention. A profile extending in afirst direction 4 is firstly produced by means of machining (grinding,milling). The profile grinding or profile milling is then repeated in asecond direction 5, whereby the surface structure shown in FIG. 3 isproduced.

FIG. 4A is a schematic sectional view of the brake lining shown in FIG.3 along the line II. The profile shape formed in the second directionmay be seen in this sectional view. The surface profile 7 of thefriction lining layer 3 is produced in this case by initially planegrinding away a portion of the worn friction lining layer and thenproducing the illustrated recesses with partially perpendicular sidewalls. The preceding plane grinding eliminates the non-uniform wear(oblique wear) of the surface of the friction lining layer 3 whichpotentially occurred in the course of operation. The obliquely wornsurface of the old friction lining layer is shown by a chain-dotted line6. The intermediate layer disposed between the friction lining layer 3and lining carrier 2 has not been shown in FIG. 4A.

FIG. 4B is a sectional view through the brake lining after applying thefresh friction lining layer 9. The layer of bonding agent appliedbetween the old friction lining layer 3 and fresh friction lining 9 isnot shown. It is generally so thin that it is not visible incross-section on the illustrated scale.

In alternative embodiments of the method in accordance with theinvention the machining process for producing the three-dimensionalsurface profile can be modified so that different surface regions of themachined friction lining layer are provided with different surfaceprofiles. The surface profiles can point in different directions indifferent regions or sections of the surface of the friction lininglayer. The surface profile structure is selected in dependence on theshape and the material of the friction lining layer, the nature of theapplication of the bonding agent, the process by which the freshfriction lining composition is pressed on and the loadings during use ofthe brake lining.

What is claimed is:
 1. A method of regenerating brake lining having afraction lining layer, said friction lining layer having a worn surface,said method comprising the steps of: maching said worn surface of saidfriction lining in such a way that a three-dimensionally profiledsurface of said friction lining layer is formed; and coating saidprofiled surface with a bonding agent and pressing thereon a freshfriction lining composition so as to form an inner surface of said freshfriction lining composition, said inner surface having a shapecomplementary of said profiled surface of said friction lining layer,whereby a regenerated friction lining layer is formed.
 2. The method ofclaim 1, wherein said machining step comprises at least one materialremoving step ina first direction substantially parellel to said wornsurface thereby forming a first plurality of parellel grooves in theworn surface.
 3. The method as claim 2, wherein said grooves are formedin a shape which is at least one of meander-shape, saw tooth-shape andtrapezoidal shape.
 4. The method as claim 2, wherein following saidfirst machining step said worn surface is machined in a second directiontransverse to said first direction, whereby a second plurality ofparellel grroves crossing said first plurality of grooves is formed. 5.The method as claim 1, wherein at least one maching step is selectedfrom the group consisting of coarse grinding, profile grinding andprofile milling.
 6. The method as claim 2, wherein said first directionis transverse to a direction of a main loading of the friction lininglayer during a braking process.
 7. The method as claim 6, wherein saidmachining step further comprises a second material removing step in eachof a plurality of portions of the worn surface wherein the direction ofthe second material removing step differs from said firts directionthereby forming a second plurality of grooves in each of the pluralityof portions of the worn surface.
 8. The method as claim 8, wherein saidmachining step comprises a coarse grinding in a first direction suchthat an irregular surface structure with substantially elongate recessesis produced, said recesses extending, at least in sections,substantially in said first direction.
 9. The method of claim 8, whereinsaid maching step is repeated in a second direction transverse to saidfirst direction.
 10. The method as claim 8, wherein said first directionis transverse to a direction of a main loading of the friction lininglayer during a braking process.
 11. The method as claim 10, wherein saidmachining step further comprises a second material removing step in eachof a plurality of portions of the worn surface wherein the direction ofthe second material removing step differs from said first directionthereby forming a second plurality of grooves in each of the pluralityof portions of the worn surface.
 12. The method as claim 1, wherein saidprofiled surface comprises a profile depth in a range of about 1 to 30mm.
 13. The method as claim 8, wherein said profile depth is in a rangeof about 5 to 20 mm.
 14. The method as claim 1, wherein said frictionlining layer is fastened to a metal sheet, said machining stepcomprising machining said friction lining layer down to a predeterminedresidual thickness such that said metal sheet constitutes, together withthe remainder of said machined friction lining layer, a sufficientlymechanically stable structure for the caoting and pressing steps. 15.The method as claim 1, wherein said bonding agent comprises a phenolresin or a rubber.
 16. The method as claim 2, wherein said firstdirection is at a right angle to a direction of a main loading of thefriction lining layer during a braking process.
 17. The method as claim8, wherein said first direction is at a right angle to a direction of amain loading of the friction lining layer during a braking process.